This invention relates generally to a high capacity, wide latitude of sheet characteristics feeder for an electrophotographic printing machine and, more particularly, concerns a variable acceleration take-away roll (TAR) for the feeder.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrophotographic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, reimaged and developed for each color separation. This charging, imaging, developing and recharging, reimaging and developing, all followed by transfer to paper, is done in a single revolution of the photoreceptor in so-called single pass machines, while multipass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color. In single pass color machines and other high speed printers, it is desirable to feed a wide variety of media for printing thereon. A large latitude of sheet sizes and sheet weights, in addition to various coated stock and other specialty papers must be fed at high speed to the printer.
In accordance with one aspect of the present invention, there is provided a sheet feeding apparatus, comprising a sheet stack support a feed head adjacent said sheet stack support for feeding sheets inseriatum from the top of the stack and a stack height sensor, wherein said stack height sensor detects a plurality of stack height zones and generates signals indicative thereof.
In accordance with yet another aspect of the invention there is provided an electrophotographic printing machine having a sheet feeder comprising a sheet stack support, a feed head adjacent said sheet stack support for feeding sheets inseriatum from the top of the stack and a stack height sensor, wherein said stack height sensor detects a plurality of stack height zones and generates signals indicative thereof.